Preparation Of ?-C₃N₄-Based Nanocomposites And Study On Their Photocatalytic Performance

Traditional energy sources(coal,oil,and natural gas)are non-renewable energy sources.Decomposing water in the sunlight to produce hydrogen is a renewable strategy.It can not only replace traditional energy sources,but also avoid environmental pollution caused by fuel combustion.At present,titanium dioxide(TiO₂)and MXene have received more and more attention as photocatalytic water catalytic materials.Improving the performance of them has become a hot topic for scientific research.Owing to the limitation of the forbidden band width of titanium dioxide,the catalytic performance cannot be well exerted.Therefore,reducing the forbidden band width of the material is considered to be one of the most effective and simple methods to directly improve the full spectrum catalytic performance of the material.The instability of MXene also limits its application in the field of photocatalysis.C₃N₄ modified nanophotocatalysts have significantly narrower forbidden band widths and have the ability to photocatalytically hydrolyze in the full spectrum or even under visible light.In addition,C₃N₄ materials also have high thermal stability and chemical stability.Therefore,this paper designed and synthesized C₃N₄ modified titanium dioxide(TiO₂)and MXene,and further studied the photocatalytic performance of the materials.In the process of utilizing solar energy conversion,TiO₂,as a typical wide band gap semiconductor(3.2 eV),has a high recombination ratio of photoelectron and hole pairs,and the main absorbance in the UV spectral range is also seriously hindered its practical application in the ultraviolet spectrum.Doping non-metal elements has proven to be a viable method.In this work,a?-C₃N₄ layer was formed in the outer layer of TiO₂by a simple method.The bandwidth of TiO₂ is greatly reduced,the redox potential is more negative than that of hydrogen generation,and it is more positive than that of oxygen generation.Therefore,the overall water-splitting effect of the Z-system in the full spectrum(200-700 nm)is better.Compared with pure TiO₂ nanotubes,the photogenerated carrier density is increased to approximately 2.4 times(TiO₂:8.8×10¹⁷?TiO₂/C₃N₄:2.1×10¹⁸ cm^-3).In addition,the production of hydrogen and oxygen by TiO₂/C₃N₄ nanotubes under the full spectrum has increased by about 13times,of which TOF(Time of flight refers to the number of conversion reactions per catalytic active center(active site)per unit time)It reached 4472.8 h^-1,which is much higher than the results reported in literature in the study of materials with similar systems.MXene samples with excellent lamellar 2D structure were also prepared.The MXene material was modified by pyrolysis deposition of ethylenediamine to obtain MXene/C₃N₄ with catalytic properties.We found that in the absence of precious metal promoters and sacrificial agents,the material achieved overall water decomposition under the full spectrum.When the sample was 0.05 g,the hydrogen production rate was108.3?mol·g^-1·h^-1,and the oxygen production rate was 64.8?mol·g^-1·h^-1.Under the photocurrent test conditions,it was confirmed that the sample with C₃N₄ superstructure greatly inhibited the photogenerated electron and hole recombination,and also showed that MXene/C₃N₄ has better carrier separation ability.The study also found that the sample had a high photocurrent density before being illuminated,indicating that the application of MXene materials not only has great advantages in battery conductivity,but also has broad application prospects and research value in new energy electric vehicles.